How do you write Prefix DR or Dr for non medical PhD holder?

It's generally not appropriate to use "Dr." or "PhD" as a prefix for someone who holds a PhD in a non-medical field. Here's why:

* Confusion: Using "Dr." for someone with a PhD in, for example, history or engineering, could be mistaken for a medical doctor, leading to confusion and potentially inappropriate interactions.

* Respect for Medical Professionals: Using "Dr." exclusively for medical doctors is a way to acknowledge and respect the specific training and responsibilities of the medical profession.

* Professional Courtesy: In academic and professional settings, it's more common to use the individual's full name or title, such as "Professor [Last Name]" or "[Full Name], PhD."

Instead of using "Dr.", you can use these options:

* Full name: "Dr. [Last Name]" can be used when referring to a PhD holder in any field, but it's not generally a prefix.

* Formal title: "Professor [Last Name]," "Dr. [Last Name], PhD," or "[Full Name], PhD" are appropriate options.

* Informal title: "Dr. [Last Name]" or "[Last Name], PhD" may be used in informal settings, but it's always best to err on the side of formality.

Remember: Always be respectful of the individual's preferred title and address them accordingly.